The present disclosure relates to image forming apparatuses such as a copy machine, a printer, a facsimile and the like, more particularly, to an image forming apparatus that includes a developing device and an image carrier unit which are removably mounted in the image forming apparatus.
In a conventional image forming apparatus, because of life of a photosensitive drum (image carrier), when the number of printed sheets reaches a predetermined number (e.g., several dozens of thousands of sheets), it is necessary to replace a drum unit (image carrier unit) that includes the photosensitive drum. Besides, also there is a case where maintenance and replacement of a developing device disposed adjacently to the drum unit are required.
Here, a developing roller of the developing device is disposed to be in contact with or near the photosensitive drum. Because of this, when replacing the drum unit or the developing device, there is a risk that the photosensitive drum and the developing roller could contact each other to damage surfaces of the photosensitive drum and the developing roller.
Accordingly, various mechanisms are devised, in which the photosensitive drum and the developing device are mountable and demountable with ease, and for example, a structure is known, in which a process cartridge (image forming unit) integrating the photosensitive drum and the developing device is mountable in and demountable from an image forming apparatus main body.
Besides, an image forming apparatus is known, which includes a roller contact-separation mechanism that prevents the photosensitive drum and the developing roller from being damaged when replacing the drum unit or the developing device. This image forming apparatus includes a holder member (drum positioning unit) on which a positioning plate for positioning a drum shaft of the photosensitive drum is mounted; after the developing device is mounted in the image forming apparatus main body, the developing roller is made to contact the photosensitive drum in accordance with a closing operation of the holder member, and the developing roller is made to evacuate from the photosensitive drum in accordance with an opening operation of the holder member.